How to Find Directrix of Parabola?

For (y^2 = 4ax), the directrix is (x = -a)

For (y^2 = -4ax), the directrix is (x = a)

For (x^2 = 4ay), the directrix is (y = -a)

For (x^2 = -4ay), the directrix is (y = a)

For ((y-k)^2 = 4a(x-h)), the directrix is (x = h-a)

For ((y-k)^2 = -4a(x-h)), the directrix is (x = h+a)

For ((x-h)^2 = 4a(y-k)), the directrix is (y = k-a)

For ((x-h)^2 = -4a(y-k)), the directrix is (y = k+a)

Identify the vertex ((h,k))

Identify the value of (a)

Use the parabola’s standard form to write the directrix equation